【 Weak current College 】 LCD technology details 】

On the LCD

Substances has three States: solid, liquid and gas.

In 1888, Australia plant scholar Lenny Crvenkovski (Reinitzer) study of cholesterol in the role of plants with Cholic PCB test, accidentally discovered the LCD, but the practical application of liquid until the 1950s began. As the name implies, the LCD is a solid-liquid between a middle class status. LCD is an organic compound, at a certain temperature range, it has a liquid flow, viscosity, deformation and other mechanical properties and heat with crystals (thermal), light (optical anisotropy), electricity (electro-optic effect), magnetic (magneto-optical effect), and other physical properties. The path of light penetrating the LCD by constitute its molecules are arranged. The charge was found to the LCD will change its molecular arrangement, thereby causing distorted or refraction of light.

Molecular arrangement of liquid crystal follow, divided into three types: Crystal particles of clay are called near crystalline (Smectic) LCD, similar fine match sticks called Nematic (Nematic) LCD, similar to cholesterol-called cholesteric liquid crystal (Cholestic). The three types of physical properties of liquid crystals are different for LCD monitor is the second type of Nematic Liquid Crystal (Nematic).

LCD principle

Only through understanding its structure and principle, understand its technology and process features, you can purchase targeted, in application and maintenance more scientific and rational. LCD is an organic compound consisting of long Rod-like molecules. In the natural state, the rod-like molecules long axis roughly parallel. LCD is the first character must be liquid poured into two columns have fine grooves in the plane to work properly. The two plane slot mutually perpendicular (90 degree intersections), that is, if a plane elements arranged in a North-South, another plane of molecules, and to arrange things in two planes between the molecules areforced into a 90-degree turn around the State. Because the light along the molecular arrangement directions, so the light through the LCD is also being reversed by 90 degrees. But when the LCD on a voltage, the molecular would be vertically so that each light out, without any change. LCD of the second characteristic is that it relies on polarization filters and light itself, the natural light is diffused in all random, polarization filter is actually a series of increasingly fine parallel lines. These lines to form a network, blocking the lines parallel and not all the light, the polarization filter line coincides with the first vertical, it can completely block those already polarized light. Only two filter line completely parallel, or light itself has been reversed to the second polarization filter match, Ray was able to penetrate. This LCD is composed of two vertical polarisation filter, so in normal circumstances should block all attempts to penetration of light. However, since both filters are filled with distortions between the LCD, so the light to wear out the first filter, it will be liquid crystal molecules turn 90 degrees from the second filter to wear out. On the other hand, in the case of a liquid crystal with a voltage, the molecular will reorder and completely parallel to the light no longer reverse, so just being the second filter blocked. In short, the power will light block does not power the light. Of course, you can change the arrangement of liquid crystal in an LCD, so that the light at power shot, without being interrupted during power-on. But due to the LCD screen is almost always lit, so the only power the light blocking "programme to achieve the most power.

Classification of LCD

You can set the LCD is divided into passive and active technology, representative products are DSTN (double-layersupertwistnematic double Super Twisted Nematic) and TFT (thin film transistor thinfilmtransistor). DSTN has always been a passive notebook monitor standards, HPA and CSTN is passive technology improvements. HPA is also called high performance addressed or quick DSTN. HPA and CSTN are better than DSTN provides better contrast and brightness. CSTN response times have now fallen to 100ms and 140 degrees viewing angle.

DSTN are super twisted nematic display (STN) developed, DSTN dual scan technologies, STN display effect is thus significantly improved. Laptop just appears mainly use STN. STN's reaction time is slower, usually around user 300ms can feel the tail (persistence). Because DSTN neck and two screens simultaneously scan in use might display a light appears to the central line.

Active-matrix display through thin-film transistors directly addressed, and this is the technical name of origin, that is, TFT (thin film transistor). Active matrix TFT belonging to LCD, reaction time is greatly improved, has reached the 25ms. It has a higher contrast ratio and a richer color. Relative DSTN, TFT features each pixel configuration a semiconductor switch component, its processing technology similar to LSI. Since each pixel can be directly controlled by point pulse, so each node relatively independent and continuous control, which not only improves the response time, while the grayscale control can be very precise, this is a TFT color DSTN more realistic reasons. At present most laptop manufacturers mainstream products are based on the TFT display.

LCD and CRT (traditional Panel) comparisons and considerations when buying

LCD works we introduced, then introduce the CRT, then we better comparison. CRT works by filament, cathode, composed of gun control gate, after power cathode filament heating, excited, emits electron flow, electron flow is with high voltage internal metal layers of acceleration, after lens formation of very fineElectron beam, hit the screen, so that the light-emitting phosphors. Electron beam deflection coil produces a magnetic field, you can control the size of screen at the specified location, the electron beam to play after the screen on a luminous point, several light-emitting points can be composed of images. RGB tricolor fluorescent points are different strength of electron beam hits, will produce a variety of color, by controlling the electron beam intensity and on/off, you can create a variety of colorful pictures. General SM-picture tube inside a layer like a sieve of net cover, electron beam through the mesh play arranged in triangular dots, three gun corresponding RGB tricolor, so called "three shots three bundles" CRT. Grill-picture tube (e.g. telilong and diamond Vicky) principle is the same, except that this class picture tube screen cover is fixed many raster portrait of the box.

Then there is the detail they differ:

Resolution
Resolution is a very important performance indicators. It refers to the screen horizontally and vertically to display the number of points (the line is displayed on the screen and the surface is composed of dots) of the number, the higher the resolution, the same screen can hold more information. For one to be able to supports 1280 x 1024 resolution, regardless of the CRT is 320x240 or 1280x1024 resolution, will be able to compare the perfect show it (because the electron beam can be flexibly adjusted). But it's maximum resolution may not be the most appropriate resolution, because if a 17 inch monitor to 1280x1024 resolution, WINDOWS fonts will be very small, over time the eye fatigue, so it is easy for 17-inch monitor is the best resolution to 1024 x 768.

But on the LCD, is not. LCD for maximum resolution is its native resolution, which is the best resolution. Once the resolution is less than the actual resolution (for example 15-inch LCD, its native resolution of 1024 x 768, but Windows setting resolution is 800 x 600), there will be two types of display modes. One is centered in the middle of the only LCD 800x600 points will display image, others not to point does not glow, keep the dark background, the picture is centered zoom out. Another is the extended display, will use this way to the screen every pixel, but because the pixels are easily distorted, so be sure to display the effect caused. So anyway in select LCD when resolution is better but appropriate use.

Refresh rate
For CRT, graphic image on the screen by one hit by electron beam and glowing fluorescent dots, because CRT Phosphor by electron beam struck in the rear light time is short, so the electron beam must constantly hit the continue emitting phosphors. Gun from the upper-left corner of the screen, the first row (row number according to the resolution of the monitor at that time, such as the decision 800X600 resolution, scanning electron gun to 600 lines), from left to right, deinterlace, first row scan finished and then from the second row of the leftmost start to the second row of the rightmost to scan the entire screen and then from the upper-left corner of the screen, then completes an on screen refresh cycle. So we can understand why the higher the resolution of the monitor, it can achieve the maximum refresh rate is low. Generally, the screen's refresh rate to achieve the above, the human eye 75HZ is not easy to feel out the screen blinks, CRT monitor refresh rate is determined by its row frequency and at the time of the resolution, the higher the same row frequency resolution, the higher the refresh rate; while row frequency certain cases, the higher the resolution, it can achieve a lower refresh rate. For LCD, there is no question of refresh rate, it simply does not need to be refreshed. Because each pixel in an LCD has continuously led until the voltage changes in light and was sent to the controller, the LCD will not have the "keep charging and discharging" flashing phenomenon.

Angle of view
At present most flat screen monitor in order to achieve the angle of view 180 °, that is, from the screen before any direction can clearly see the display. While the LCD is different, it's the Visual angle is based on advanced technology, part of the new and different products in the Visual angle has been able to reach about 160, 180 degree Achilles CRT has been very close. There are also some LCD while nominal angle of 160 degrees, but in fact it does not meet this standard. Users in the use process once the perspective beyond its actual visual range, screen color will diminish, Darken, or even appear as become negative image. Most likely everyone for Philips advertising misled by LCD perspective and in fact is not very large, rather than a small number of CRT, is an obvious place than CRT weakest, so don't worry about being colleagues saw xiaoben bear's middle name. Of course, if the manufacturer of the product in the perspective of technology, increase will better. The following introduction.

TN + Film (TN + perspective expanding membrane) technology
Structurally, the LCD using the LCD as the display materials. LCD is a cross between solid and liquid substances between, temperatures will be showing a transparent liquid state and cooling later become cloudy with crystalline particles of solid state. Molecular arrangement of liquid crystal under three different: similar Smectic liquid crystal clay-like, similar fine match rods of Nematic Liquid Crystal, similar to cholesterol-Cholestic LCD,. These three LCD's physical characteristics are different, are typically used for LCD monitor is the second type of Nematic Liquid Crystal, the adoption of such liquid crystal manufacturing LCD monitor also known as LCD (LiquidCrystalDisplay). Ordinary LCD liquid crystal molecules in the upper flow is horizontal, the lower of liquid crystal molecules are arranged vertically, and is located on the lower level of the liquid crystal molecules near the top that is horizontally, close to the lower of the blinking vertical arrangement. Overall look, LCD subChild are arranged like a spiral rotation, but expandedbased on the angle of TN + Film Technology LCD liquid crystal molecules are arranged vertically on the screen, so that the upper surface with a special film to increase Visual angle. Technically, this technology is based on a mature standard TFT-TwistedNematic (twist Nematic) LCD technology. As long as the upper surface of the substrate, plus a layer of special films (turning film) it can be horizontal angle increased from 90 ° to 140 °. The advantages of this technology is self-evident, it is relatively cheap and the development of a more mature technology, the high rate of finished products. But the disadvantage of this technique is equally obvious that the contrast is low and respond slower inherent shortcomings still no qualitative change.

IPS (plate switch orSuper-TFT) technology
IPS or "plate switch" technology first by Hitachi (Hitachi) developed by NEC and now Nokia (Nokia) have also adopted this technology TFT production.

Principle:
IPS and TN + Film (twist Nematic LCD + perspective expanding film combination) technology for maximum difference is the orientation of liquid crystal molecules is parallel to the substrate instead of the normal to the substrate. This is achieved through voltage.
Using IPS or technology enables angle SuperTFT extended to 170 degrees, basically can reach CRT monitor-like perspective. But this technique also have disadvantages, because liquid crystal molecular orientation, making the comb-shaped electrodes must be made out, placed in the lower glass substrate, not the same as in TN mode (forming a TN LCD usually include glass, ITO film, with the film, polarizing plates, made of plywood, a total of two layers, called the upper and lower layers, each layer contains the electrode and assigned to the film formation of Groove and dissection is the liquid crystal molecules), housed in two layers of glass substrate. Doing so will reduce the contrast, backlight must therefore be increased to meet the required brightness. With TN + Film (TN + perspective expanding membrane) technology the same IPS mode of contrast and response time compared with traditional TFT-TN also has not improved significantly.

3MVA (Multi-DomainVerticalAlignment, more regional vertically) technology
MVA technology is developed by Fujitsu company. From a technical perspective, the MVA moment should be LCD wide angle and short response time is the best solution. MVA technology enables Visual angle can reach 160 °, response time of up to 20ms. In MVA technology, M represents the multi-domain "refers to a single color unit with protruding objects inside it to form a number of areas. VA representative "VerticalAlignment (vertically), due to the projection, liquid crystal molecules in static and not entirely arranged vertically. When the voltage produced electric field, the liquid crystal molecules become horizontally, so that the back light light passes through the various layers. MVA technology can provide perspective than TN + extended membrane technology and IPS Technology faster response time, video and game performance is very important. Also increase the contrast, but with perspective.

TN + Film (TN + perspective expanding membrane) technology
Low-cost, high yield, the Visual angle 140 degrees, contrast, and response time without much improvement. IPS (internal switch orSuper-TFT) technologies: the Visual angle of 170 degrees, contrast and response time is much improved. MVA (Multi-DomainVerticalAlignment, more regional vertically) technology Visual angle of 160 degrees, contrast, and response time are enhanced, suitable for video and gaming playback.

Visual area
Visual area means in practice that can be used to display the part of the image area of the screen. Because the size of a CRT monitor is actually the size of the picture tube, can be used to display the image of some fundamental to this size, because the CRT's borders make up part of the space. Generally, the 17-inch CRT monitor Visual area in 15.8-16 inches or so, and 15 inch monitor Visual area only 13.8 ". But for LCD, nominal size is basically the size of the viewable area, the space used by the border is very small, 15-inch LCD in the Visual area of approximately 14.5 around, this is why LCD looks better than the same size larger CRT. So when purchasing LCD 15 village can basically be enough.

Brightness and contrast
LCD display features mainly have a backlight lights, the brightness of the light source determines the entire LCD screen brightness and color saturation. Theoretically, the LCD brightness is the higher the better, the brightness of the unit of measurement for cd/m2 (per meter square candle), also called NIT lumens. TFT screen brightness is now mostly beginning from 150Nits started, normally 200Nits can show a better picture. Contrast that is black and white two color contrast measurement at different levels. Contrast ratio 120: 1 you can show a lively, rich color (because the human eye can discern contrasts in about 100: 1 or so), the ratio of up to 300: 1, it can support various bands of color. At present most of the LCD monitor's contrast ratio is 100: 1 ~ 300: 1 cent. Currently, there is not a fair value of standard to measure the brightness and contrast contrast value, purchase the LCD on a pair of sharp eyes. So pay attention to when choosing LCD this indicator, it is also the LCD product performance difference between the largest ring estimated purchase some difficulty.

Reaction speed
Measuring the rate of reaction time in milliseconds (ms), refers to a pixel-by-turnDark and the dark turn two. This value as small as possible, the smaller the number, description, the faster response. Current mainstream LCD response in General, over 25ms commercial purpose (such as word processing or text processing) and nothing is too big, because such uses do not have to be too concerned about the response time of LCD. But if you are used to play games, watch a VCD/DVD, full screen high speed dynamic images, reaction time is especially important, if response time is long, then the picture will appear smearing, blur, etc. Take a simple example, the market most LCD monitors playing QUAKE3 is have varying degrees of tail phenomenon, in particular high speed updates the screen. While CRT is not the problem, because the CRT 1ms response time only, absolutely no tail phenomenon.

Color
When it comes to color CRT, LCD or not, in theory, CRT display of color with a TV is infinite. While the LCD display only approximately 26 million colors, most products are claimed to be able to display 1677 million colors (16777216 color, 32-bit), but in fact are dithering algorithm (dithering), and a true 32-bit color is very large compared to the gap, so expressive of the color and the transition still and traditional CRT. By the same token, the LCD in the performance of the gray-scale capacity as CRT. All conditional can compare: find a 17 inch CRT monitor telilong, then put on a 15-inch LCD that displays both an image of 1677 million colors. CRT display screen is very bright, but the LCD is some "fake", although it cannot be said to go wrong, but watching is not that long tube of the CRT.

Show results
First, the vast majority of CRT based consumer CRT varying degrees there are focused, convergence, respiration and other issues, and manufacturers of technology are inseparable. If the manufacturer of the relevant control circuit design is advanced, are easy to occur earlier. This is why the same are telilong kinescope, SONY original factory production of monitors and other manufacturers are very different from the production of display performance. While the LCD is no focus, and so on, because it simply does not need to be focused. However online-and non-linear distortion, LCD or CRT, it appears more likely to occur.

Radiation
Because CRT display of light through the cathode tubes, also issued a radiation, so it is very harmful to the human body, but later TCO9X requirement is CRT in this regard has been greatly improved. But the LCD as it works, when the work will not be issued a little radiation, strong than CRT. So in average family or to use the CRT more appropriate, multimedia effects will be better and the price is relatively cheap, LCD flat panel monitor more suitable for commercial use, stock trading, media editing more suitable for the use of LCD.